Making a single node using multiple nodes
This is quite simple. All you have to do is to create a group from the nodes.

Simple example:

Say you have some fancy node setup:



To group these nodes, select those you want to group (press B to border select ). Then in the nodes menu select Node > Make Group (or press Ctrl+G):



After having created the group, connect the input sockets you want to have as input (here the color to diffuse shader):



To get out of your group click on the little up arrow at the bottom:



(Or press the Tab key)

Et voilà, you have a fancy shader:



Hope that helps